1. Field of the Invention
The invention relates to an apparatus for performing colorimetric determinations of liquids.
Colorimetry is a much-used technique in analytical chemistry and involves measuring the concentration of a colored component in a liquid by passing light of a certain wave-length, preferably attuned to the maximum extinction (light absorption) of the component to be determined, through the liquid under study and comparing the intensity of the transmitted light with the intensity of light transmitted by a blank. The absorption thus determined is a measure of the concentration of the component in the liquid under study.
2. Description of the Prior Art
In conventional colorimeters, samples of the liquid having a colored component whose concentration is to be determined have to be placed in cuvettes specially intended for such a purpose. This represents a substantial disadvantage in those determinations which must be performed frequently, partly because it prevents or hampers the automatization of such methods. Consequently, apparatus have become available for the determination of colorimetric reactions directly in the test tubes in which reactions have optionally been performed giving rise to situations in which it is desirable to perform a colorimetric determination in the test liquid itself to obtain further information about the nature and the course of the reaction concerned.
A known apparatus designed for this purpose, consists of a source of white light, a flexible light-guide formed of a bundle of thin glass filaments, an optical filter, a photoelectric cell with an amplifier, and a digital monitor. The flexible light-guide is divided into two compartments, one for transport of light from the light-source to the test liquid, the other for transport of the light transmitted by the liquid to be measured to the photo-electric cell, after the light has passed through the optical filter. A portion of the white light passed along the light-guide is reflected by a mirror which is placed at a set distance from the end of the light-guide. When measuring the light-absorption of the liquid under investigation, the end of the light-guide and the mirror are immersed in the liquid under investigation. Therefore, the space between the end of the light-guide and the mirror is filled with the liquid under investigation while the length of the light-path in the liquid remains constant due to the fixed distance between the mirror and the end of the light-guide. The reflected light is led to an optical filter by the second compartment of the light-guide, such that the measuring apparatus is preferably attuned to that wavelength at which the liquid under investigation shows a maximum light absorption. The intensity of the reflected and filtered light is then measured by the photo-electric cell. Comparison of the intensity of the reflected, filtered light from the liquid under investigation with that of a blank allows the light absorption of the liquid under investigation to be determined, and this may then be read from the digital monitor.
The disadvantage of this type of colorimetric determination apparatus is that the end of the flexible light-guide fitted with the mirror has to be repeatedly immersed in the liquid under investigation, which requires an effective washing procedure after each measurement to prevent mutual influence affecting the measurements obtained with various test liquids.